tailieunhanh - Báo cáo Y học: Effect of coenzymes and thyroid hormones on the dual activities of Xenopus cytosolic thyroid-hormone-binding protein (xCTBP) with aldehyde dehydrogenase activity

A cytosolic thyroid-hormone-binding protein (xCTBP), predominantly responsible for the major binding activity of T3 in the cytosol of Xenopus liver, has been shown to be identical to aldehyde dehydrogenase class 1 (ALDH1) [Yamauchi, K., Nakajima, J., Hayashi, H., Horiuchi, R. & Tata, . (1999) J. Biol. Chem. 274, 8460–8469]. Within this paper we surveyed which signaling, and other, compounds affect the thyroid hormone binding activity and aldehyde dehydrogenase activity of recombinant Xenopus ALDH1 (xCTBP/xALDH1) while examining the relationship between these two activities | Eur. J. Biochem. 269 2257-2264 2002 FEBS 2002 doi Effect of coenzymes and thyroid hormones on the dual activities of Xenopus cytosolic thyroid-hormone-binding protein xCTBP with aldehyde dehydrogenase activity Kiyoshi Yamauchi and Jun-ichiro Nakajima Department of Biology and Geoscience Faculty of Science Shizuoka University Shizuoka Japan A cytosolic thyroid-hormone-binding protein xCTBP predominantly responsible for the major binding activity of T3 in the cytosol of Xenopus liver has been shown to be identical to aldehyde dehydrogenase class 1 ALDH1 Yamauchi K. Nakajima J. Hayashi H. Horiuchi R. Tata . 1999 J. Biol. Chem. 274 8460-8469 . Within this paper we surveyed which signaling and other compounds affect the thyroid hormone binding activity and aldehyde dehydrogenase activity of recombinant Xenopus ALDH1 xCTBP xALDH1 while examining the relationship between these two activities. NAD and NADH each 200 M and two sseroids 20 M inhibit significantly the T3-binding activity while nAdH and NADPH each 200 M and iodothyronines 1 M inhibit the ALDH activity. Scatchard analysis and kinetic studies of xCTBP xALDH1 indicate that NAD and T3 are noncompetitive inhibitors of thyroid-hormone-binding and ALDH activit ies respectively. These results indicate the formation of a ternary complex consisting of the protein NAD and thyroid hormone. Although the in vitro studies indicate that NAD and NADH markedly decrease T3-binding to xCTBP xALDH1 at w 10 4 M a concentration equal to the NAD content in various Xenopus tissues photoaffinitylabeling of 125I T3 using cultured Xenopus cells demonstrates xCTBP xALDH1 bound T3 within living cells. These results raise the possibility that an unknown factor s besides NAD and NADH may modulate the thyroid-hormone-binding activity of xCTBP xALDH1. In comparison thyroid hormone at its physiological concentration would poorly modulate the enzyme activity of xCTBP xALDH1. Keywords cytosolic .